Tunable spectral filtration device

Abstract

A tunable spectral filtration device is disclosed that includes one or more pairs of interference filters in series, wherein each element of each pair is independently selected from one or more options, independently positioned to intersect a path of converging or diverging light, and independently tilted with respect to the light path. Each filter may be either of a bandpass type, a shortpass type, a longpass type, a notch type, or multiple combinations thereof. Each filter in the series may be independently selected and tilted to tune the net spectral output of the series. The elements in a pair of filters may be tilted in opposite directions so as to cancel angle-of incidence dependent broadening of the spectral output of the individual filters for noncollimated light, as well as cancel translational shift of the transmitted light rays. The elements in a pair of filters may be tilted through orthogonal tilt axes so as to cancel polarization dependent broadening of the spectral output of the individual filters for light whose polarization state is a superposition of nonzero parallel and perpendicular components relative to the tilt axes.

1 . A tunable spectral filtration device, comprising:
 a first optical substrate coated with a multilayer interference coating thereby comprising a first filter;   a second optical substrate coated with a multilayer interference coating, thereby comprising a second filter;   the first filter and the second filter being positioned in series to intersect a light path of converging or diverging light having an axis, thereby creating a filter pair; and   the first filter and the second filter being independently tiltable with respect to the axis in order to vary the transmitted wavelengths through the filter pair by canceling angle-of-incidence dependent broadening or polarization dependent broadening, or both.   
     
     
         2 . The device of  claim 1 , wherein the first filter is tilted by the same amount as the second filter, is tilted along a tilt axis parallel to the tilt axis of the second filter, and is tilted in the opposite direction as the second filter, to cancel angle-of-incidence dependent broadening of the spectral output of the individual filters for converging or diverging light. 
     
     
         3 . The device of  claim 1 , wherein the first filter is tilted by the same amount as the second filter and is tilted along a tilt axis perpendicular to the tilt axis of the second filter, to cancel polarization dependent broadening of the spectral output of the individual filters for light whose polarization state is a superposition of nonzero parallel and perpendicular components relative to the tilt axes. 
     
     
         4 . The device of  claim 1 , wherein the first filter and the second filter have equivalent construction, thereby comprising a matched filter pair. 
     
     
         5 . The device of  claim 4 , wherein the first filter is tilted by the same amount as the second filter, is tilted along a tilt axis parallel to the tilt axis of the second filter, and is tilted in the opposite direction as the second filter, to cancel angle-of-incidence dependent broadening of the spectral output of the individual filters for converging or diverging light. 
     
     
         6 . The device of  claim 4 , wherein the first filter is tilted by the same amount as the second filter and is tilted along a tilt axis perpendicular to the tilt axis of the second filter, to cancel polarization dependent broadening of the spectral output of the individual filters for light whose polarization state is a superposition of nonzero parallel and perpendicular components relative to the tilt axes. 
     
     
         7 . The device of  claim 4 , wherein the number of layers required to attain adequate depth of blocking is distributed between the first filter and the second filter. 
     
     
         8 . The device of  claim 1 , wherein the first filter is tilted in the opposite direction as the second filter to cancel translational shift of the axis of the transmitted light path. 
     
     
         9 . The device of  claim 1 , wherein one or both of the first and second filters are mounted in filter selection members and are selectable from collections of filters mounted in the selection members. 
     
     
         10 . The device of  claim 9 , wherein the selection members are wheels that are rotatable in a plane and tiltable with respect to the plane. 
     
     
         11 . The device of  claim 9 , wherein the selection members are sliders that are translatable in a plane and tiltable with respect to the plane. 
     
     
         12 . The device of  claim 1 , wherein the light path is the output from a light source, wherein the light source is a light emitting diode, a multicolor light emitting diode, a phosphor-coated light emitting diode, a halogen lamp, or a xenon lamp. 
     
     
         13 . The device of  claim 1 , wherein the light path is the input to a light detector, wherein the light detector is a photodiode, a film camera, a digital camera, or a digital video camera. 
     
     
         14 . A tunable spectral filtration device comprising:
 a first plurality of input optical filters, each of the first plurality comprising a substrate coated with a multilayer interference coating, the first plurality being positioned in series to intersect an axis of a light path;   a second plurality of output optical filters, each of the second plurality comprising a substrate coated with a multilayer interference coating, the second plurality being positioned in series to intersect the axis; and   the second plurality of output filters being interleaved with the first plurality of input filters thereby creating a third plurality of filter pairs, each filter in each filter pair of the third plurality being independently tiltable with respect to the axis in order to vary the transmitted wavelengths through the third plurality of filter pairs.   
     
     
         15 . The device of  claim 14 , wherein the input filter and the output filter in one or more of the third plurality of filter pairs have equivalent construction, thereby comprising one or more matched filter pairs. 
     
     
         16 . The device of  claim 15 , wherein the input filter is tilted by the same amount as the output filter in one or more of the matched filter pairs, along a tilt axis parallel to the tilt axis of the output filter in one or more of the matched filter pairs, and in the opposite direction as the output filter in one or more of the matched filter pairs, to cancel angle-of-incidence dependent broadening of the spectral output of the individual filters for converging or diverging light. 
     
     
         17 . The device of  claim 15 , wherein the input filter is tilted by the same amount as the output filter in one or more of the matched filter pairs, along a tilt axis perpendicular to the tilt axis of the output filter in one or more of the matched filter pairs, to cancel polarization dependent broadening of the spectral output of the individual filters for light whose polarization state is a superposition of nonzero parallel and perpendicular components relative to the tilt axes. 
     
     
         18 . The device of  claim 14 , wherein the input filters and the output filters in two or more of the filter pairs all have equivalent construction thereby comprising one or more matched super pairs of two or more matched filter pairs. 
     
     
         19 . The device of  claim 18 , wherein both of the matched filter pairs in one or more of the super pairs comprise the input filters that are tilted by the same amount as the output filters, along a tilt axis parallel to the tilt axis of the output filters, and in the opposite direction as the output filters, to cancel angle-of-incidence dependent broadening of the spectral output of the individual filters for converging or diverging light. 
     
     
         20 . The device of  claim 19 , wherein one of the matched filter pairs in one or more of the super pairs comprises filters that are tilted along a tilt axis perpendicular to the tilt axis of the filters comprising the other of the matched filter pairs to cancel polarization dependent broadening of the spectral output of the individual filters for light whose polarization state is a superposition of nonzero parallel and perpendicular components relative to the tilt axes. 
     
     
         21 . The device of  claim 15 , wherein the number of layers required to attain adequate depth of blocking in a matched filter pair is distributed between the input filter and the output filter. 
     
     
         22 . The device of  claim 14 , wherein one or more of the input filters are tilted in the opposite direction as the corresponding output filters to cancel translational shift of the axis of the transmitted light path. 
     
     
         23 . The device of  claim 14 , wherein one or more of the input and output filters are mounted in filter selection members and are selectable from collections of filters mounted in the selection members. 
     
     
         24 . The device of  claim 23 , wherein one or more of the filter selection members are wheels that are rotatable in a plane and tiltable with respect to the plane. 
     
     
         25 . The device of  claim 23 , wherein one or more of the filter selection members are sliders that are translatable in a plane and tiltable with respect to the plane. 
     
     
         26 . The device of  claim 14 , wherein the light path is the output from a light source, wherein the light source is a light emitting diode, a multicolor light emitting diode, a phosphor-coated light emitting diode, a halogen lamp, or a xenon lamp. 
     
     
         27 . The device of  claim 14 , wherein the light path is the input to a light detector, wherein the detector is a photodiode, a film camera, a digital camera, or a digital video camera.